Control circuit, control method and power converter

ABSTRACT

A control circuit for controlling a power converter can include: a constant voltage output module, a constant current output module, and a power stage circuit; and where the control circuit is configured to select one of a first feedback signal representative of output information of the constant current output module, and a second feedback signal representative of output information of the constant voltage output module as a feedback input signal based on operation states of the constant current output module and the constant voltage output module, in order to control a switching state of a power switch of the power stage circuit.

RELATED APPLICATIONS

This application claims the benefit of Chinese Patent Application No.201910937813.6, filed on Sep. 30, 2019, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of powerelectronics, and more particularly to control circuits, control methods,and associated power converters.

BACKGROUND

A switched-mode power supply (SMPS), or a “switching” power supply, caninclude a power stage circuit and a control circuit. When there is aninput voltage, the control circuit can consider internal parameters andexternal load changes, and may regulate the on/off times of the switchsystem in the power stage circuit. Switching power supplies have a widevariety of applications in modern electronics. For example, switchingpower supplies can be used to drive light-emitting diode (LED) loads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an example power converter with aconstant current output module and a constant voltage output module.

FIG. 2 is a schematic block diagram of an example feedback circuit.

FIG. 3 is a schematic block diagram of an example compensation circuit.

FIG. 4 is a schematic block diagram of a first example power converterwith a control circuit, in accordance with embodiments of the presentinvention.

FIG. 5 is a schematic block diagram of a first example control circuit,in accordance with embodiments of the present invention.

FIG. 6 is a schematic block diagram of a second example power converterwith a control circuit, in accordance with embodiments of the presentinvention.

FIG. 7 is a schematic block diagram of an example current controlcircuit, in accordance with embodiments of the present invention.

FIG. 8 is a schematic block diagram of a second example control circuit,in accordance with embodiments of the present invention.

FIG. 9 is a schematic block diagram of a third example control circuit,in accordance with embodiments of the present invention.

FIG. 10 is a schematic block diagram of a fourth example controlcircuit, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION

Reference may now be made in detail to particular embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention may be described in conjunction with thepreferred embodiments, it may be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents that may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it may be readilyapparent to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knownmethods, procedures, processes, components, structures, and circuitshave not been described in detail so as not to unnecessarily obscureaspects of the present invention.

The power requirements for various types of load devices can vary widelyat many applications. For example, most load devices require a constantvoltage. However, there are also load devices that require a constantcurrent. To facilitate design, the power converter can provide dualoutput that include a constant voltage output and a constant currentoutput.

Referring now to FIG. 1, shown is a schematic block diagram of anexample power converter with a constant current output module and aconstant voltage output module. As used herein, a “module” can becircuitry, such as including hardware devices, elements, structures,components, and/or circuits. This example power converter can beconfigured as a flyback converter that can provide energy for theconstant current output module and the constant voltage output module.The constant current output module can include an LED drive circuitconnected in series with LEDs. The LED drive circuit can control thecurrent flowing through the LED to be a constant current. The constantvoltage output module can generate a constant voltage. A feedbackcircuit of the flyback converter can receive feedback signals from thesecondary side of the flyback converter, and may generate a controlsignal at the primary side of the flyback converter to control theswitching state of a power switch of a power stage circuit in theflyback converter, in order to regulate the output signals of theconstant current output module and the constant voltage output module.

Referring now to FIG. 2, shown is a schematic block diagram of anexample feedback circuit. This example feedback circuit can receivefeedback signals that are provided by the constant current output moduleand the constant voltage output module. For example, the feedbackcircuit can receive the feedback signals that can include input signalVin of the constant voltage output module, input signal VLED+ of theconstant voltage output module, voltages at cathodes of the LED stringsand a compensation signal generate by a compensation circuit, and cangenerate the control signal based on the feedback signals to control theswitching state of the power switch.

Referring now to FIG. 3, shown is a schematic block diagram of anexample compensation circuit. The compensation circuit can include aminimum circuit and a transconductance operational amplifier. A firstinput terminal of the transconductance operational amplifier can receivea minimum value of the voltages at cathodes of the LED strings (e.g.,voltages Vled1-, Vled2-, Vled3-, Vled4-), and a second input terminal ofthe transconductance operational amplifier can receive reference voltageVref. An output terminal of the transconductance operational amplifiercan connect to a RC circuit for generating the compensation signal. Thefeedback circuit can include multiple RC circuits, which may cause thefeedback loop circuit to form multiple poles, resulting in poor systemstability. Further, the feedback circuit can be more complicated withmultiple components, and the cost of the system is high. The feedbackcircuit may employ the input signal of the constant voltage outputmodule as a main feedback signal, and employ the voltages at cathodes ofthe LED strings and the compensation signal as auxiliary feedbacksignals. This can cause the limited ability of voltages at cathodes ofthe LED strings and the compensation signal to control the flybackconverter. In this way, when the LED is light, the voltages at thecathodes of all LED strings are significantly higher than referencevoltage Vref, possibly resulting in greater energy loss.

In one embodiment, a control circuit for controlling a power convertercan include: (i) a constant voltage output module, a constant currentoutput module, and a power stage circuit; and (ii) where the controlcircuit is configured to select one of a first feedback signalrepresentative of output information of the constant current outputmodule, and a second feedback signal representative of outputinformation of the constant voltage output module as a feedback inputsignal based on operation states of the constant current output moduleand the constant voltage output module, in order to control a switchingstate of a power switch of the power stage circuit.

Referring now to FIG. 4, shown is a schematic block diagram of a firstexample power converter with a control circuit, in accordance withembodiments of the present invention. This example power converter caninclude power stage circuit 1, constant current output module 2,constant voltage output module 3, and control circuit 4. Power stagecircuit 1 can provide energy to constant current output module 2 andconstant voltage output module 3. Control circuit 4 can select one of afirst feedback signal representative of the output information ofconstant current output module 2 and a second feedback signalrepresentative of the output information of constant voltage outputmodule 3 as a feedback input signal, based on the operation states ofconstant current output module 2 and constant voltage output module 3,in order to control the switching state of the power switch of powerstage circuit 1. Further, control circuit 4 can receive the feedbackinput signal to generate a feedback output signal, and control theswitching state of the power switch of power stage circuit 1 based onthe feedback output signal, thereby controlling the energy provided forconstant current output module 2 and constant voltage output module 3.

In one example, when constant current output module 2 and constantvoltage output module 3 operate simultaneously, control circuit 4 canselect the first feedback signal as the feedback input signal. Inanother example, when constant current output module 2 is in anon-operating state (e.g., disabled), and constant voltage output module3 is in an operating state, control circuit 4 can select the secondfeedback signal as the feedback input signal, in order to control aninput voltage of constant voltage output module 3 to be not less than aset value, and to ensure the stability of the output voltage of constantvoltage output module 3.

In one example, when constant current output module 2 and constantvoltage output module 3 operate simultaneously, control circuit 4 canselect the minimum value of the first feedback signal and the secondfeedback signal as the feedback input signal. This can avoid thesituation that the input voltage of constant voltage output module 3 istoo low at the unsteady state (e.g., switching the operation state ofconstant current output module 2 and constant voltage output module 3,or switching the load), thereby ensuring that constant voltage outputmodule 3 can operate normally.

Referring now to FIG. 5, shown is a schematic block diagram of a firstexample control circuit, in accordance with embodiments of the presentinvention. This example control circuit 4 can include selection module41, feedback module 42, and control module 43. Selection module 41 canselect one of a first feedback signal representative of the outputinformation of constant current output module 2 and a second feedbacksignal representative of the output information of constant voltageoutput module 3 as a feedback input signal, based on the operationstates of constant current output module 2 and constant voltage outputmodule 3. Feedback module 42 can receive the feedback input signal togenerate a feedback output signal. Control module 43 can control theswitching state of the power switch of power stage circuit 1 based onthe feedback output signal, in order to regulate input signals ofconstant current output module 2 and constant voltage output module 3.

In one example, power stage circuit 1 can include a power stage circuitincluding a transformer with at least two secondary windings. Forexample, the two secondary windings can be wound on the same magneticcore. The two secondary windings can respectively wound on differentmagnetic cores. Constant voltage output module 3 can be coupled to afirst secondary winding, and can include a DC-DC converter that mayreceive an input voltage to generate a constant output voltage. Constantcurrent output module 2 can be coupled to a second secondary winding,and may include at least one current branch that can include a load anda current control circuit coupled in series. The current control circuitcan control a current flowing through a corresponding load to beconstant. When constant current output module 2 includes N currentbranches, the N current branches can be connected in parallel, whereN≥2.

In one example, power stage circuit 1 can include a power stage circuitincluding a center-tapped transformer. Constant voltage output module 3can be coupled to one of a high potential and a center-tapped terminalsof the center-tapped transformer, and can include a DC-DC converter thatmay receive an input voltage to generate a constant output voltage. Theconstant current output module can be coupled to the other of the highpotential and the center-tapped terminals of the center-tappedtransformer, and may include at least one current branch that caninclude a load and a current control circuit coupled in series. Thecurrent control circuit can control a current flowing through acorresponding load to be constant. When constant current output module 2includes N current branches, the N current branches can be connected inparallel, where N≥2.

In addition, the first feedback signal may be a maximum value of voltagedrops across the loads, and the second feedback signal may be a samplingsignal representative of the input voltage of the constant voltageoutput module. Further, the first feedback signal may be a minimum valueof voltages at low potential terminals of the loads, and the secondfeedback signal may be the sampling signal representative of the inputvoltage of the constant voltage output module. In this example, thenumber of turns N1 of the secondary winding corresponding to constantcurrent output module 2 and the number of turns N2 of the secondarywinding corresponding to constant voltage output module 3 may be set tomeet a predetermined relationship. In this way, constant voltage outputmodule 3 can operate normally when constant current output module 2operates at light load, and when constant current output module 2 isdisabled.

In particular embodiments, the control circuit can select one of thefirst feedback signal representative of the output information of theconstant current output module and the second feedback signalrepresentative of the output information of the constant voltage outputmodule as the feedback input signal based on the operation states of theconstant current output module and the constant voltage output module,thereby controlling the switching state of the power switch of the powerstage circuit based on the feedback output signal to provide energy forthe constant current output module and the constant voltage outputmodule. When the constant current output module and the constant voltageoutput module operate simultaneously, the control circuit selects thefirst feedback signal or the minimum value of the first feedback signaland the second feedback signal as the feedback input signal. When theconstant voltage output module is operating, and the constant currentoutput module is disabled, the control circuit can select the secondfeedback signal as the feedback input signal. This example method canselect only one feedback input signal to control the power stage circuitunder certain operating condition, and simplify the circuit, therebyreducing the number of the components and the cost, improving thestability and of the system, and solving the problem of energy lossunder the condition of light load.

In FIG. 4, the example power converter can include power stage circuit1, constant current output module 2, constant voltage output module 3and control circuit 4. Power stage circuit 1 can provide energy toconstant current output module 2 and constant voltage output module 3.Control circuit 4 can select one of a first feedback signalrepresentative of the output information of constant current outputmodule 2 and a second feedback signal representative of the outputinformation of constant voltage output module 3 as a feedback inputsignal, based on the operation states of constant current output module2 and constant voltage output module 3, in order to control theswitching state of the power switch of power stage circuit 1. Further,control circuit 4 can receive the feedback input signal to generate afeedback output signal, and control the switching state of the powerswitch of power stage circuit 1 based on the feedback output signal,thereby controlling the energy provided for constant current outputmodule 2 and constant voltage output module 3.

Referring now to FIG. 6, shown is a schematic block diagram of a secondexample power converter with a control circuit, in accordance withembodiments of the present invention. This example power converter caninclude power stage circuit 1, constant current output module 2,constant voltage output module 3 and control circuit 4. Power stagecircuit 1 can be configured as a flyback power stage circuit includingtwo secondary windings. Constant voltage output module 3 can connect tosecondary winding Ns1, and constant voltage output module 3 can connectto secondary winding Ns2. Constant current output module 2 can includefour current branches connected in parallel with each other, and each ofthe current branches can include a load and a current control circuitconnected in series, and the current control circuit can control acurrent flowing through the corresponding load to be constant. Here, theload may be a light-emitting diode (LED), or an LED string includingmultiple LEDs connected in series. Constant voltage output module 3 caninclude a DC-DC converter which can convert input voltage Vin intoconstant output voltage Vout. In one example, the DC-DC converter can beconfigured as a buck converter, and the buck converter can adopt controlmethods such as peak current control, valley current control and so on,which is not limited in the present invention. In another example, theDC-DC converter may be other converters such as a boost converter, whichis not limited in the present invention. This example power convertercan further include a constant current and voltage control circuit,which can control the current control circuits in constant currentoutput module 2 and the DC-DC converter in constant voltage outputmodule 3 based on a pulse-width modulation (PWM) signal.

In one example, control circuit 4 can include selection module 41,feedback module 42, and control module 43. Selection module 41 canselect one of a first feedback signal representative of the outputinformation of constant current output module 2 and a second feedbacksignal representative of the output information of constant voltageoutput module 3 as a feedback input signal, based on the operationstates of constant current output module 2 and constant voltage outputmodule 3. Further, the first feedback signal can be configured as theminimum value of voltages at low potential terminals of the loads (e.g.,voltages Vled1-, Vled2-, Vled3-, Vled4-), and the second feedback signalcan be configured as sampling signal V2 that is generated by dividinginput voltage Vin sensed at an input terminal of constant voltage outputmodule 3. Control module 43 can control the switching state of the powerswitch of power stage circuit 1 based on the feedback output signal, inorder to regulate input signals of constant current output module 2 andconstant voltage output module 3.

In one example, selection module 41 can include switch S1, switch S2,and a minimum circuit. The minimum circuit can receive the voltages atthe low potential terminals of the loads, and generate the minimum valueof voltages at low potential terminals of the loads. An output terminalof the minimum value circuit can connect to an output terminal ofselection module 41 via switch S1. One terminal of switch S2 can receivesampling signal V2, and the other terminal of switch S2 can connect tothe output terminal of selection module 41. Selection module 41 cangenerate an feedback output signal based on the feedback input signal atthe output terminal thereof. In this example, a voltage divide caninclude resistors Rv3 and Rv2 connected in series between input voltageVin and the ground, and can divide input voltage Vin to generatesampling signal V2 at a common terminal of resistors Rv3 and Rv2.

Further, signals LED_on and LED_off can be generated based on theoperation states of constant current output module 2 and constantvoltage output module 3. When constant current output module 2 andconstant voltage output module 3 operate simultaneously, signal LED_oncan be active, and signal LED_off can be inactive, such that switch S1controlled by signal LED_on can be turned on, and switch S2 controlledby signal LED_off can be turned off. In this way, control circuit 4 canselect the first feedback signal that is the minimum value of voltagesat low potential terminals of the loads as the feedback input signal. Inanother example, when constant current output module 2 is in anon-operating state, and constant output module 3 is in an operatingstate, signal LED_off can be active, and signal LED_on can be inactive,such that switch S1 controlled by signal LED_on can be turned off, andswitch S2 controlled by signal LED_off can be turned on. In this way,control circuit 4 can select the second feedback signal that is samplingsignal V2 as the feedback input signal.

In one example, feedback module 42 can include optocoupler OPC1.Feedback module 42 can generate a compensation signal according to thefeedback input signal, and convert the compensation signal into thefeedback output signal via optocoupler OPC1. Feedback module 42 canfurther include transconductance operational amplifier GM1 and capacitorC1. A non-inverting input terminal of transconductance operationalamplifier GM1 can receive the feedback input signal, and an invertinginput terminal of transconductance operational amplifier GM1 can receivereference voltage Vref. An output terminal of transconductanceoperational amplifier GM1 can connect to one terminal of capacitor C1,and the other terminal of capacitor C1 can be grounded via resistor Rc1.The compensation signal that is generated at the output terminal oftransconductance operational amplifier GM1 can control a primary sidecurrent of optocoupler OPC1, thereby controlling a secondary sidecurrent of optocoupler OPC1 to generate the feedback output signal. Inaddition, the change tendency of the feedback output signal can beconsistent with the change tendency of the compensation signal.

Feedback module 42 can also include transistor Qf1 and resistor R1. Acontrol terminal of transistor Qf1 can connect to the output terminal oftransconductance operational amplifier GM1. The primary side ofoptocoupler OPC1 and transistor Qf1 are connected in series between afirst supply voltage and ground, resistor R1 and the secondary side ofoptocoupler OPC1 are connected in series between a second supply voltageand ground, and the feedback output signal can be generated at thecommon terminal of resistor R1 and the secondary side of optocouplerOPC1. Here, the first supply voltage can be configured as input voltageVin of the constant voltage output module or output voltage Vout of theconstant voltage output module, and the second supply voltage can beconfigured as set voltage Vpref. Control circuit 4 can further includeresistor Rf1 connected to the first supply voltage, resistor Rf2connected in series with transistor Qf1 for limiting the current, andcapacitor Cf1 connected between the common terminal of resistor R1 andthe secondary side of optocoupler OPC1 and ground.

Referring now to FIG. 7, shown is a schematic block diagram of anexample current control circuit, in accordance with embodiments of thepresent invention. Constant current output module 2 can include fourcurrent branches connected in parallel with each other, and each of thecurrent branches can include an LED string and a current control circuitconnected in series. The control circuit can control the current flowingthrough the corresponding LED string to be constant. In this example,taking LED string LED1 as an example, the current control circuit caninclude transistor Qr1, resistor Rs1 and operational amplifier OP1. LEDstring LED1, transistor Qr1, and resistor Rs1 can connect in seriesbetween input voltage Vled+ of constant current output module 2 and theground. A first input terminal of operational amplifier OP1 can connectto a common terminal of transistor Qr1 and resistor Rs1, a second inputterminal of operational amplifier OP1 can receive reference voltageVsref, and an output terminal of operational amplifier OP1 can connectthe control terminal of transistor Qr1. It should be understood that thecurrent control circuit can alternatively be implemented in other ways,which can control the current flowing through the corresponding LEDstring to be constant.

Referring now to FIG. 8, shown is a schematic block diagram of a secondexample control circuit, in accordance with embodiments of the presentinvention. With respect to FIG. 6, the difference here is the structureof the feedback module. This example feedback module 42 can includeoptocoupler OPC2. Feedback module 42 can generate a compensation signalaccording to the feedback input signal, and convert the compensationsignal into the feedback output signal via optocoupler OPC2. Feedbackmodule 42 can also include transconductance operational amplifier GM1and capacitor C1. An inverting input terminal of transconductanceoperational amplifier GM1 can receive the feedback input signal, and anon-inverting input terminal of transconductance operational amplifierGM1 can receive reference voltage Vref. An output terminal oftransconductance operational amplifier GM1 can connect to one terminalof capacitor C1, and the other terminal of capacitor C1 can be groundedvia resistor Rc1. The compensation signal that is generated at theoutput terminal of transconductance operational amplifier GM1 cancontrol a primary side current of optocoupler OPC2, thereby controllinga secondary side current of optocoupler OPC2 to generate the feedbackoutput signal.

In addition, the change tendency of the feedback output signal can beopposite to the change tendency of the compensation signal. Feedbackmodule 42 can also include transistor Qf2 and resistor R2. A controlterminal of transistor Qf2 can connect to the output terminal oftransconductance operational amplifier GM1. The primary side ofoptocoupler OPC2 and transistor Qf2 can connect in parallel between afirst supply voltage and ground, resistor R2 and the secondary side ofoptocoupler OPC2 may be connected in series between a second supplyvoltage and ground, and the feedback output signal can be generated atthe common terminal of resistor R2 and the secondary side of optocouplerOPC2. Here, the first supply voltage can be configured as input voltageVin of the constant voltage output module or output voltage Vout of theconstant voltage output module, and the second supply voltage can beconfigured as set voltage Vpref. Control circuit 4 can also includeresistor Rf3 connected to the first supply voltage, resistor Rf4connected in series with resistors Rf3, Rf5, and Rf6 connected in serieswith transistor Qf2 for limiting the current, and capacitor Cf2connected between the common terminal of resistor R2 and the secondaryside of optocoupler OPC2 and ground.

Referring now to FIG. 9, shown is a schematic block diagram of a thirdexample control circuit, in accordance with embodiments of the presentinvention. With respect to FIG. 6, the difference here is the structureof the selection module. This example selection module 41 can includeswitches S1 and S2, and a minimum circuit. The minimum circuit canreceive the voltages at the low potential terminals of the loads andsampling signal V2 representative of an input voltage of the constantvoltage output module, and generate the minimum value of voltages at lowpotential terminals of the loads and sampling signal V2. An outputterminal of the minimum circuit can connect to an output terminal ofselection module 41 via switch S1. One terminal of switch S2 can receivesampling signal V2, and the other terminal of switch S2 can connect tothe output terminal of selection module 41. Selection module 41 cangenerate an feedback output signal based on the feedback input signal atthe output terminal.

Further, signals LED_on and LED_off can be generated based on theoperation states of the constant current output module 2 and constantvoltage output module 3. When constant current output module 2 andconstant voltage output module 3 operate simultaneously, signal LED_oncan be active, and signal LED_off can be inactive, such that switch S1controlled by signal LED_on can be turned on, and switch S2 controlledby signal LED_off can be turned off. In this way, control circuit 4 canselect the first feedback signal that is the minimum value of voltagesat low potential terminals of the loads and sampling signal V2 as thefeedback input signal. In another example, when constant current outputmodule 2 is in a non-operating state, and constant voltage output module3 is in an operating state, signal LED_off can be active, and signalLED_on can be inactive, such that switch S1 controlled by signal LED_oncan be turned off, and switch S2 controlled by signal LED_off can beturned on. In this way, control circuit 4 can select the second feedbacksignal that is sampling signal V2 as the feedback input signal. This canavoid the situation that the input voltage of constant output module 3is too low at the unsteady state (e.g., switching the operation state ofconstant current output module 2 and constant voltage output module 3,or switching the load), thereby ensuring that constant voltage outputmodule 3 can operate normally.

Referring now to FIG. 10, shown is a schematic block diagram of a fourthexample control circuit, in accordance with embodiments of the presentinvention. With respect to FIG. 9, the difference here is the structureof the feedback module. This example feedback module 42 can includeoptocoupler OPC2. Feedback module 42 can generate a compensation signalaccording to the feedback input signal, and convert the compensationsignal into the feedback output signal via optocoupler OPC2. Feedbackmodule 42 can also include transconductance operational amplifier GM1and capacitor C1. An inverting input terminal of transconductanceoperational amplifier GM1 can receive the feedback input signal, and anon-inverting input terminal of transconductance operational amplifierGM1 can receive reference voltage Vref. An output terminal oftransconductance operational amplifier GM1 can connect to one terminalof capacitor C1 and the other terminal of capacitor C1 can be groundedvia resistor Rc1. The compensation signal that is generated at theoutput terminal of transconductance operational amplifier GM1 cancontrol a primary side current of optocoupler OPC2, thereby controllinga secondary side current of optocoupler OPC2 to generate the feedbackoutput signal. In addition, the change tendency of the feedback outputsignal can be opposite to the change tendency of the compensationsignal.

Feedback module 42 can also include transistor Qf2 and resistor R2. Acontrol terminal of transistor Qf2 can connect to the output terminal oftransconductance operational amplifier GM1. The primary side ofoptocoupler OPC2 and transistor Qf2 are connected in parallel between afirst supply voltage and ground, resistor R2 and the secondary side ofoptocoupler OPC2 are connected in series between a second supply voltageand ground, and the feedback output signal can be generated at thecommon terminal of resistor R2 and the secondary side of optocouplerOPC2. Here, the first supply voltage can be configured as input voltageVin of the constant voltage output module or output voltage Vout of theconstant voltage output module, and the second supply voltage can beconfigured as set voltage Vpref.

Particular embodiments can also include a control method of controllinga power converter. The power converter can include a constant voltageoutput module, a constant current output module, and a power stagecircuit. The control circuit may select one of a first feedback signalrepresentative of output information of the constant current outputmodule, and a second feedback signal representative of outputinformation of the constant voltage output module as a feedback inputsignal based on operation states of the constant current output moduleand the constant voltage output module, in order to control a switchingstate of a power switch of the power stage circuit.

In one example, when the constant current output module and the constantvoltage output module operate simultaneously, the control circuit canselect the first feedback signal as the feedback input signal. In oneexample, when the constant current output module and the constantvoltage output module operate simultaneously, the control circuit canselect a minimum value of the first feedback signal and the secondfeedback signal as the feedback input signal. In one example, the powerconverter may be configured as a flyback converter.

In one example, the power stage circuit include a power stage circuitincluding a transformer with at least two secondary windings. Theconstant voltage output module can be coupled to a first secondarywinding, and can include a DC-DC converter that may receive an inputvoltage to generate a constant output voltage. In addition, the constantcurrent output module can be coupled to a second secondary winding, andmay include at least one current branch that can include a load and acurrent control circuit coupled in series. The current control circuitcan control a current flowing through a corresponding load to beconstant. When constant current output module 2 includes N currentbranches, the N current branches can be connected in parallel, whereN≥2.

In one example, power stage circuit 1 can include a power stage circuitincluding a center-tapped transformer. Constant voltage output module 3can be coupled to one of a high potential and a center-tapped terminalsof the center-tapped transformer, and may include a DC-DC converter thatmay receive an input voltage to generate a constant output voltage. Theconstant current output module can be coupled to the other of the highpotential and the center-tapped terminals of the center-tappedtransformer, and may include at least one current branch that caninclude a load and a current control circuit coupled in series. Thecurrent control circuit can control a current flowing through acorresponding load to be constant. When constant current output module 2includes N current branches, the N current branches can be connected inparallel, where N≥2.

For example, the first feedback signal may be a maximum value of voltagedrops across the loads, and the second feedback signal may be a samplingsignal representative of the input voltage of the constant voltageoutput module. Further, the first feedback signal may be a minimum valueof voltages at low potential terminals of the loads, and the secondfeedback signal may be the sampling signal representative of the inputvoltage of the constant voltage output module.

The embodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with modifications as are suited to particularuse(s) contemplated. It is intended that the scope of the invention bedefined by the claims appended hereto and their equivalents.

1.-20. (canceled)
 21. A control circuit for controlling a powerconverter, the power converter comprising a constant voltage outputmodule, a constant current output module, and a power stage circuithaving a transformer, wherein: a) the constant current output comprisesa DC-DC converter that is configured to receive a first input voltagegenerated by a first secondary winding of the transformer to generate aconstant output voltage; b) the constant current output module comprisesat least one current branch that is configured to receive a second inputvoltage generated by a second secondary winding of the transformer; andc) the control circuit is configured to receive a first feedback signalrepresentative of output information of the constant current outputmodule, and a second feedback signal representative of outputinformation of the constant voltage output module and generate afeedback output signal, in order to control a switching state of a powerswitch of the power stage circuit.
 22. The control circuit of claim 21,wherein the control circuit is configured to select one of the firstfeedback signal and the second feedback signal as a feedback inputsignal based on operation states of the constant voltage output moduleand the constant current output module.
 23. The control circuit of claim22, wherein when the constant current output module and the constantvoltage output module operate simultaneously, the control circuitselects the first feedback signal as the feedback input signal.
 24. Thecontrol circuit of claim 22, wherein when the constant current outputmodule and the constant voltage output module operate simultaneously,the control circuit selects a minimum value of the first and secondfeedback signals as the feedback input signal.
 25. The control circuitof claim 22, wherein when the constant voltage output module operates,and the constant current output module is disabled, the control circuitselects the second feedback signal as the feedback input signal.
 26. Thecontrol circuit of claim 21, wherein the control circuit is configuredto receive the first input voltage and voltage drops across the loads ofthe constant current output module.
 27. The control circuit of claim 21,wherein the control circuit comprises: a) a selection module configuredto select one of the first feedback signal and the second feedbacksignal as the feedback input signal based on the operation states of theconstant current output module and the constant voltage output module;b) a feedback module configured to receive the feedback input signal togenerate the feedback output signal; and c) a control module configuredto control the switching state of the power switch based on the feedbackoutput signal, in order to regulate input signals of the constantcurrent output module and the constant voltage output module.
 28. Thecontrol circuit of claim 21, wherein the constant current output modulecomprises N current branches coupled in parallel with each other, eachof the N current branches comprises a load and a current control circuitcoupled in series, and the current control circuit is configured tocontrol a current flowing through a corresponding load to be constant,wherein N is a positive integer.
 29. The control circuit of claim 21,wherein the first feedback signal is configured to be a maximum value ofvoltage drops across the loads of the constant current output module,and the second feedback signal is configured to be a sampling signalrepresentative of the first input voltage of the constant voltage outputmodule.
 30. The control circuit of claim 21, wherein the first feedbacksignal is configured to be a minimum value of voltages at low potentialterminals of the loads of the constant current output module, secondfeedback signal is configured to be a sampling signal representative ofthe first input voltage of the constant voltage output module.
 31. Thecontrol circuit of claim 27, wherein the selection module comprises: a)a minimum circuit having an output terminal coupled to an outputterminal of the selection module via a first switch, and beingconfigured to receive voltages at low potential terminals of loads ofthe constant current output module, or to receive voltages at lowpotential terminals of loads of the constant current output module and asampling signal representative of the first input voltage of theconstant voltage output module; and b) a second switch having a firstterminal for receiving the sampling signal, and a second terminalcoupled to the output terminal of the selection module.
 32. The controlcircuit of claim 31, wherein: a) when the constant current output moduleand the constant voltage output module operate simultaneously, the firstswitch is turned on, and the second switch is turned off; and b) whenthe constant voltage output module operates, and the constant currentoutput module is disabled, the first switch is turned off, and thesecond switch is turned on.
 33. The control circuit of claim 27, whereinthe feedback module is configured to generate a compensation signalbased on the feedback input signal, and to generate the feedback outputsignal base on the compensation signal.
 34. control circuit of claim 33,wherein the change tendency of the feedback output signal is consistentwith the change tendency of the compensation signal.
 35. The controlcircuit of claim 33, wherein the change tendency of the feedback outputsignal is opposite to the change tendency of the compensation signal.36. The control circuit of claim 33, wherein the feedback module furthercomprises: a) a transconductance operational amplifier having a firstinput terminal for receiving the feedback input signal, a second inputterminal for receiving a reference voltage, and being configured togenerate the compensation signal at an output terminal thereof; b) afirst capacitor coupled to the output terminal of the transconductanceoperational amplifier; and c) an optocoupler having a primary sidecurrent that is controlled based on the compensation signal, therebycontrolling a secondary side current of the optocoupler to generate thefeedback output signal.
 37. The control circuit of claim 36, wherein thefeedback module further comprises: a) a first transistor having acontrol terminal coupled to the output terminal of the transconductanceoperational amplifier, and being coupled in series with a primary sideof the optocoupler between a first supply voltage and a groundreference; b) a first resistor coupled in series with a secondary sideof the optocoupler between a second supply voltage and a groundreference; and c) wherein the feedback output signal is generated at acommon terminal of the first resistor and the secondary side of theoptocoupler.
 38. The control circuit of claim 36, wherein the feedbackmodule further comprises: a) a first transistor having a controlterminal coupled to the output terminal of the transconductanceoperational amplifier, and being coupled in parallel with a primary sideof the optocoupler between a first supply voltage and a groundreference; b) a first resistor coupled in series with a secondary sideof the optocoupler between a second supply voltage and a groundreference; and c) wherein the feedback output signal is generated at acommon terminal of the first resistor and the secondary side of theoptocoupler.
 39. A power converter, comprising the control circuit ofthe claim 21, wherein: a) the constant voltage output module isconfigured to generate the constant output voltage; b) the constantcurrent output module is configured to provide a constant current for aload; and c) the power stage circuit is configured to provide energy forthe constant voltage output module and the constant voltage outputmodule.
 40. The power converter of the claim 39, wherein the powerconverter is configured as a flyback converter.